Bump maven-plugin from 6.3.0 to 6.4.0

Bumps [maven-plugin](https://github.com/freefair/gradle-plugins) from 6.3.0 to 6.4.0.
- [Release notes](https://github.com/freefair/gradle-plugins/releases)
- [Commits](freefair/gradle-plugins@6.3.0...6.4.0)

---
updated-dependencies:
- dependency-name: io.freefair.gradle:maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

build.gradle

@@ -6,7 +6,7 @@ buildscript {
  }
  dependencies {
  classpath 'com.android.tools.build:gradle:7.1.1'
- classpath 'io.freefair.gradle:maven-plugin:6.3.0'
+ classpath 'io.freefair.gradle:maven-plugin:6.4.0'
  }
 }